Method for robust wireless monitoring and tracking of solar trackers in commercial solar power plants

ABSTRACT

For each first tracker in a first subset there exists a respective second tracker in a second subset such that a distance between the first tracker and the second tracker is shorter than each distance between the second tracker and each of the other first trackers in the subset by more than a threshold distance. In a first time slot, data is wirelessly transmitted using a same first frequency from each of the first trackers in the subset of the first trackers to the respective second tracker in the subset of the second trackers. In a subsequent time slot, the data is wirelessly transmitted from each of the second trackers in the subset of the second trackers to a final destination data collector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to wireless monitoring, and, more particularly, towireless monitoring of solar trackers.

2. Description of the Related Art

A typical commercial solar plant consists of several thousands of solartrackers. For optimal performance, trackers may point to the sun'sposition so as to capture a maximum amount of solar energy. Because thesun's position in the sky is constantly changing, pointing the trackersat the sun may require continuous tracking. A control station may governthe tracking by sending commands to each individual tracker over a wirednetwork. The control station may also perform continuous conditionmonitoring of the trackers by receiving status messages from thetrackers. Connecting thousands of trackers to the central controlstation via wires is a cumbersome process requiring a lot of time andincurring huge cost.

Commercial solar plants may include thousands of tracking collectors(i.e., trackers) to capture the solar energy. These tracking collectorscan convert solar energy to electricity via either of two methods. Inthe first such method, sometimes referred to as “Concentrated SolarPower” (CSP), the trackers include mirrors which focus the sun's rays ona heat collector. The heat energy is then later converted toelectricity. In the second method, sometimes referred to as“Concentrated Photovoltaic” (CPV), the trackers include photovoltaicmodules which convert solar energy to electricity directly.

For optimal performance, the trackers may continuously point in thedirection of the sun. Also, during non-operation, at night, or duringinclement weather conditions (e.g., rain, snow, etc.), the trackers mayreturn to the safe position in which they are protected. The position ofeach of these trackers may be controlled from and by a central datacontrol station (DCS) that transmits commands and receives statusmessages from the trackers using wired communication.

FIG. 1 illustrates a known wired data communication hierarchy 10 forparabolic trough CSP systems. Hierarchy 10 may include fiber-opticpoint-to-point links 12 between the DCS and the data concentrators.Hierarchy 10 may also include wired RS-485 or fiber-optic point-to-pointlinks 14 between the data concentrators and the data collectors.Hierarchy 10 may further include a tracking system 16 (e.g., “tracker”)having data collectors and hydraulic and power units for a parabolictrough.

Tracking requirements and solutions may be the same for CSPs and CPVsfrom a communications point of view. A typical solar plant includesthousands of trackers, so the plant may cover several square kilometersof area. Thus, connecting each of these trackers with a DCS may requireseveral kilometers of wire as well as a huge cost and installationeffort.

What is neither disclosed nor suggested by the prior art is a method ofcontrolling a group of solar trackers that overcomes the above-describedproblems.

SUMMARY OF THE INVENTION

A wireless solution to the above-described challenges can be both costand time effective for this commercial solar plant application. However,connecting thousands of trackers wirelessly calls for a robustcommunication method which can ensure the reliability and latencyrequirements of the application. The invention provides several suchmethods to enable robust wireless communication between the controlstation and the trackers.

The invention is directed to methods to enable robust wirelesscommunication between a control station and solar trackers in acommercial solar plant. The methods include data collection sweepingschemes for rectangular and circular grid topologies; data collectionschemes for any topology, including random slotted, hierarchical, divideand conquer, and repeaters/collectors; and data communication from adata control station to trackers.

A wireless solution can be both time and cost effective. Abi-directional wireless communication between a DCS and trackers maycall for certain data collection and data communication features. Withregard to data collection, status data may be collected securely andreliably from all trackers (of which there may be about two thousand)within a few seconds. With regard to data communication, the trackersmay be controlled for both normal operation and emergency operation. Theinvention may provide several embodiments of robust communicationmethods that satisfy the reliability and latency parameters of theabove-described two types of communication.

The invention may provide several wireless communication methods forreliable and time-constrained data transfer between a control system andtrackers for commercial solar power plants. The described methods can beused in solar tracking systems, for example.

In one embodiment, the invention provides a method for wirelessmonitoring and tracking of solar trackers in commercial solar powerplants.

Typical deployments of solar power systems may be either in rectangulargrid or circular topologies. According to one embodiment of theinvention, the geometry of tracker distribution may be used to assigntime slots as well as to assign routing schemes.

In another embodiment, sweeping schemes may be used for rectangular gridtopology. Trackers may communicate with their neighbor nodes dependentupon the selected sweeping method. Vertical sweeping may be selectedwhen the number of trackers in a column is more than the number oftrackers in a row. Horizontal sweeping may be selected when the numberof trackers in a row is more than the number of trackers in a column.Diagonal sweeping may be used when the number of trackers in a row andthe number of trackers in a column are nearly equal. The selection ofthe sweeping scheme may be optimized for frequency reuse and forcollection/communication on a single path.

In yet another embodiment, sweeping for circular topology may includedata flow being on concentric circles or directed towards the center ofthe topology. Sweeping for circular topology may also include divisionof the topology into sectors and the use of different frequency channelgroups for different sectors.

In one embodiment, a random slotted scheme may be used for any topology.All non-overlapping communication may be scheduled in a given slot, andthe use of available frequency channels may be maximized. Methods mayoptimize the use of variable slot sizes as well as the use of multiplecollection schedules.

In another embodiment, a hierarchical scheme may be used for anytopology. The whole topology may be divided into several non-overlappingclusters where trackers send data to the pre-defined/selected clusterhead. The cluster head may then forward the collected data to thecentral data control system. Methods may optimize frequency reuse aswell as the reuse of multiple radios/directional antennas forsimultaneous communication or for directly communicating with the datacontrol system.

In yet another embodiment, a divide and conquer method may be used tocollect/communicate information. The whole area of the topology may bedivided into multiple sub-areas. A different subset of channels may beused for each sub-area. It may be possible to employ a differentcommunication method for every sub-area so as to optimize the overallcommunication. A given path may be divided into multiple sectors andsimultaneous communication may be scheduled in those sectors.

In one embodiment, stand-alone repeaters or intermediate data collectorsmay be used to relay communications. Multiple radios may be used inorder to transmit communications to several nodes simultaneously.Directional antennas may be used in order to increase the transmissionrange and enable communication with other intermediate collectors orwith the final data collector.

In another embodiment, data communication from the data control system(DCS) to the trackers may be performed in the case wherein the DCS needsto communicate with a particular tracker. The same path and intermediatenodes may be used as in the case where the DCS collects data from theparticular tracker. An algorithm that determines the shortest pathdistance may be used.

In yet another embodiment, data communication from the DCS to thetrackers may be performed in the case wherein the DCS needs to broadcastthe same data to all trackers. Pre-defined clusterheads/repeaters/intermediate collectors may be used for rebroadcastingmessages. A pre-defined set of trackers may be used as broadcasters aswell.

In still another embodiment, data communication from the DCS to thetrackers may be performed in the case wherein the DCS needs to sendindividualized data to every tracker node. The same communication pathsand schedule used to transmit data from the trackers to the DCS may beused in transmitting individualized data from the DCS to the trackernodes, but in the reverse order.

The invention comprises, in one form thereof, a method of wirelesscommunication including providing a plurality of first trackers and aplurality of second trackers. A subset of the first trackers and asubset of the second trackers are determined such that for each of thefirst trackers in the subset of the first trackers there exists arespective second tracker in the subset of the second trackers such thata distance between the first tracker and the second tracker is shorterthan each distance between the second tracker and each of the otherfirst trackers in the subset by more than a threshold distance. In afirst time slot, data is wirelessly transmitted from each of the firsttrackers in the subset of the first trackers to the respective secondtracker in the subset of the second trackers. The transmitting isperformed using a same first frequency. In at least one subsequent timeslot, the data is wirelessly transmitted from each of the secondtrackers in the subset of the second trackers to a final destinationdata collector.

The invention comprises, in another form thereof, a method of wirelesscommunication including providing a matrix of wireless devices. Thematrix includes rows and columns of the wireless devices. A finaldestination data collector is provided approximately centrally locatedwithin the matrix of wireless devices. The wireless devices are groupedinto a plurality of substantially rectangular clusters. Each clusterspans at least a subset of the rows and at least a subset of thecolumns. The wireless devices in each cluster include a plurality oftrackers and a single cluster head. Data from the trackers in eachcluster is transmitted to the cluster head in the cluster. The data fromthe cluster heads is transmitted to the final destination datacollector.

The invention comprises, in yet another form thereof, a method ofwireless communication including providing a final destination datacollector and a plurality of trackers disposed to one side of the finaldestination data collector. The trackers are arranged in a sequentialdata path such that each tracker is configured to pass data to the finaldestination data collector or to an other tracker that is closer to thefinal destination data collector. The sequential data path is dividedinto a plurality of sectors. Each sector includes a subset of thetrackers. Each sector includes a far end and close end. The far end isfarther from the final destination data collector than is the close end.Transmission of data is begun substantially simultaneously from the farend of each sector toward the close end of each sector along thesequential data path. The transmission of data is continued along thesequential data path such that each tracker transmits its own data inaddition to data received from an immediately preceding tracker. Thetransmission continues until the data from a first sector that isclosest to the final destination data collector has been transmitted tothe final destination data collector. The data from a second sector thatis second closest to the final destination data collector is transmittedto the first sector. The data from the second sector is passed along thetrackers in the first sector to the final destination data collector.The trackers in the first sector refrain from adding their data to thedata from the second sector during the passing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a block diagram of a wired communication hierarchy forparabolic trough CSP systems according to the prior art.

FIG. 2 a is a plan view of a solar tracker wireless monitoring andtracking arrangement of the invention with the trackers arranged in arectangular grid.

FIG. 2 b is a plan view of a solar tracker wireless monitoring andtracking arrangement of the invention with the trackers arranged inconcentric circles.

FIG. 3 is a table of sweeping schemes of the invention for trackersarranged in a rectangular grid topology.

FIG. 4 a is a plan view of one embodiment of a vertical sweeping schemeof the invention for trackers arranged in a rectangular grid topology.

FIG. 4 b is a plan view of one embodiment of a horizontal sweepingscheme of the invention for trackers arranged in a rectangular gridtopology.

FIG. 4 c is a plan view of a first data transfer step of one embodimentof a diagonal sweeping scheme of the invention for trackers arranged ina rectangular grid topology.

FIG. 4 d is a plan view of a second data transfer step of the diagonalsweeping scheme of FIG. 4 c.

FIG. 4 e is a plan view of a third data transfer step of the diagonalsweeping scheme of FIG. 4 c.

FIG. 5 a is a plan view of data transfer in a first time slot of thevertical sweeping scheme of FIG. 4 a.

FIG. 5 b is a plan view of data transfer in a second time slot of thevertical sweeping scheme of FIG. 4 a.

FIG. 5 c is a plan view of data transfer in an (n−1)th time slot of thevertical sweeping scheme of FIG. 4 a, wherein n is the number of rows inthe rectangular grid.

FIG. 5 d is a plan view of data transfer in an nth time slot of thevertical sweeping scheme of FIG. 4 a, wherein n is the number of rows inthe rectangular grid.

FIG. 5 e is a plan view of data transfer in an (n+1)th time slot of thevertical sweeping scheme of FIG. 4 a, wherein n is the number of rows inthe rectangular grid.

FIG. 5 f is a plan view of data transfer in an (n+m−2)th time slot ofthe vertical sweeping scheme of FIG. 4 a, wherein n is the number ofrows in the rectangular grid, and m is the number of columns in therectangular grid.

FIG. 6 is a plan view illustrating a matrix of trackers divided intosub-matrices for simultaneous data transfer using the same frequencychannels in a vertical sweeping scheme of the invention.

FIG. 7 a is a plan view of data transfer in a first time slot in amethod of simultaneous data transfer using the same frequency channelsin a vertical sweeping scheme of the invention.

FIG. 7 b is a plan view of data transfer in a second time slot in themethod of FIG. 7 a.

FIG. 7 c is a plan view of data transfer in an (n−1)th time slot in themethod of FIG. 7 a.

FIG. 7 d is a plan view of data transfer in an nth time slot in themethod of FIG. 7 a.

FIG. 7 e is a plan view of data transfer in an (n+1)th time slot in themethod of FIG. 7 a.

FIG. 7 f is a plan view of data transfer in an (n+2)th time slot in themethod of FIG. 7 a.

FIG. 7 g is a plan view of data transfer in a time slot subsequent tothe (n+2)th time slot in the method of FIG. 7 a.

FIG. 7 h is a plan view of data transfer in a final time slot in themethod of FIG. 7 a.

FIG. 8 a is a plan view of data transfer in a method of data transferalong a single path with only one non-overlapping frequency channelavailable and eight trackers in the path according to one embodiment ofthe invention.

FIG. 8 b is a plan view of data transfer in a method of data transferalong a single path with only one non-overlapping frequency channelavailable and nine trackers in the path according to one embodiment ofthe invention.

FIG. 8 c is a plan view of data transfer in a method of data transferalong a single path with two non-overlapping frequency channelsavailable and eight trackers in the path according to one embodiment ofthe invention.

FIG. 8 d is a plan view of data transfer in a method of data transferalong a single path with two non-overlapping frequency channelsavailable and nine trackers in the path according to one embodiment ofthe invention.

FIG. 8 e is a plan view of data transfer in a method of data transferalong a single path with three non-overlapping frequency channelsavailable and eight trackers in the path according to one embodiment ofthe invention.

FIG. 8 f is a plan view of data transfer in a method of data transferalong a single path with three non-overlapping frequency channelsavailable and nine trackers in the path according to one embodiment ofthe invention.

FIG. 9 a is a plan view of data transfer in a first time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 b is a plan view of data transfer in a second time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 c is a plan view of data transfer in a third time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 d is a plan view of data transfer in a fourth time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 e is a plan view of data transfer in a fifth time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 f is a plan view of data transfer in a sixth time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 g is a plan view of data transfer in a seventh time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 h is a plan view of data transfer in an eighth time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 i is a plan view of data transfer in a ninth time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 j is a plan view of data transfer in a tenth time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 9 k is a plan view of data transfer in an eleventh time slot in amethod of concentric and radial data transfer using a circular gridtopology.

FIG. 10 a is a plan view of data transfer in a first time slot in amethod of radial data transfer using a circular grid topology.

FIG. 10 b is a plan view of data transfer in a second time slot in amethod of radial data transfer using a circular grid topology.

FIG. 10 c is a plan view of data transfer in a third time slot in amethod of radial data transfer using a circular grid topology.

FIG. 10 d is a plan view of data transfer in a fourth time slot in amethod of radial data transfer using a circular grid topology.

FIG. 10 e is a plan view of data transfer in a fifth time slot in amethod of radial data transfer using a circular grid topology.

FIG. 10 f is a plan view of data transfer in a sixth time slot in amethod of radial data transfer using a circular grid topology.

FIG. 10 g is a plan view of data transfer in a seventh time slot in amethod of radial data transfer using a circular grid topology.

FIG. 11 a is a plan view of data transfer in a first time slot in arandom slotted scheme of data transfer.

FIG. 11 b is a plan view of data transfer in a second time slot in arandom slotted scheme of data transfer.

FIG. 11 c is a plan view of data transfer in a third time slot in arandom slotted scheme of data transfer.

FIG. 11 d is a plan view of data transfer in a fourth time slot in arandom slotted scheme of data transfer.

FIG. 11 e is a plan view of data transfer in a fifth time slot in arandom slotted scheme of data transfer.

FIG. 11 f is a plan view of data transfer in a sixth time slot in arandom slotted scheme of data transfer.

FIG. 12 a is a plan view of data transfer in a first time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 b is a plan view of data transfer in a second time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 c is a plan view of data transfer in a third time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 d is a plan view of data transfer in a fourth time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 e is a plan view of data transfer in a fifth time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 f is a plan view of data transfer in a sixth time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 g is a plan view of data transfer in a seventh time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 h is a plan view of data transfer in an eighth time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 i is a plan view of data transfer in a ninth time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 j is a plan view of data transfer in a tenth time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 k is a plan view of data transfer in an eleventh time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 12 l is a plan view of data transfer in a twelfth time slot in arandom slotted scheme of data transfer including multiple collectionschedules.

FIG. 13 is a plan view of data transfer in a hierarchical scheme of datacollection.

FIG. 14 is a plan view of a matrix of tracker nodes divided intoquadrant sections for a divided scheme of data collection.

FIG. 15 a is a plan view of a conventional communication path and thesame communication path divided into two sections for a divided schemeof data collection.

FIG. 15 b is a plan view of a first step of data collection in theconventional communication path and in the same communication pathdivided into two sections for a divided scheme of data collection.

FIG. 15 c is a plan view of a second step of data collection in theconventional communication path and in the same communication pathdivided into two sections for a divided scheme of data collection.

FIG. 15 d is a plan view of a third step of data collection in theconventional communication path and in the same communication pathdivided into two sections for a divided scheme of data collection.

FIG. 15 e is a plan view of a fourth step of data collection in theconventional communication path and in the same communication pathdivided into two sections for a divided scheme of data collection.

FIG. 15 f is a plan view of a fifth step of data collection in theconventional communication path and in the same communication pathdivided into two sections for a divided scheme of data collection.

FIG. 15 g is a plan view of a sixth step of data collection in theconventional communication path and in the same communication pathdivided into two sections for a divided scheme of data collection.

FIG. 16 a is a plan view of a first step of data collection in twoadjacent paths which are each divided into three sectors.

FIG. 16 b is a plan view of a second step of data collection in twoadjacent paths which are each divided into three sectors.

FIG. 16 c is a plan view of a third step of data collection in twoadjacent paths which are each divided into three sectors.

FIG. 16 d is a plan view of a fourth step of data collection in twoadjacent paths which are each divided into three sectors.

FIG. 16 e is a plan view of a fifth step of data collection in twoadjacent paths which are each divided into three sectors.

FIG. 16 f is a plan view of a sixth step of data collection in twoadjacent paths which are each divided into three sectors.

FIG. 17 a is a plan view of a solar tracker wireless monitoring andtracking arrangement of the invention with the trackers arranged in arectangular grid, and including four repeater/intermediate datacollectors.

FIG. 17 b is a plan view of a solar tracker wireless monitoring andtracking arrangement of the invention with the trackers arranged in acircular grid, and including five repeater/intermediate data collectors.

FIG. 17 c is a plan view of a solar tracker wireless monitoring andtracking arrangement of the invention with the trackers arranged in arectangular grid, and including eight repeater/intermediate datacollectors.

FIG. 17 d is a plan view of a solar tracker wireless monitoring andtracking arrangement of the invention with the trackers arranged in acircular grid, and including eight repeater/intermediate datacollectors.

FIG. 17 e is a plan view of another solar tracker wireless monitoringand tracking arrangement of the invention with the trackers arranged ina rectangular grid, and including eight repeater/intermediate datacollectors.

FIG. 17 f is a plan view of another solar tracker wireless monitoringand tracking arrangement of the invention with the trackers arranged ina circular grid, and including eight repeater/intermediate datacollectors.

FIG. 18 a is a plan view of data transfer from DCS to tracker nodes in afirst time slot in a scheme in which the DCS broadcasts the same data toall tracker nodes.

FIG. 18 b is a plan view of data transfer from DCS to tracker nodes in asecond time slot in a scheme in which the DCS broadcasts the same datato all tracker nodes.

FIG. 18 c is a plan view of data transfer from DCS to tracker nodes in athird time slot in a scheme in which the DCS broadcasts the same data toall tracker nodes.

FIG. 18 b is a plan view of data transfer from DCS to tracker nodes in afourth time slot in a scheme in which the DCS broadcasts the same datato all tracker nodes.

FIG. 19 a is a plan view of individual data transfer from tracker nodesto a DCS along parallel paths in a first time slot.

FIG. 19 b is a plan view of individual data transfer from tracker nodesto a DCS along parallel paths in a second time slot.

FIG. 19 c is a plan view of individual data transfer from tracker nodesto a DCS along parallel paths in a third time slot.

FIG. 19 d is a plan view of individual data transfer from tracker nodesto a DCS along parallel paths in a fourth time slot.

FIG. 20 a is a plan view of transfer of individual data from a DCS totracker nodes along parallel paths in a first time slot.

FIG. 20 b is a plan view of transfer of individual data from a DCS totracker nodes along parallel paths in a second time slot.

FIG. 20 c is a plan view of transfer of individual data from a DCS totracker nodes along parallel paths in a third time slot.

FIG. 20 d is a plan view of transfer of individual data from a DCS totracker nodes along parallel paths in a fourth time slot.

FIG. 21 a is a plan view of another embodiment of transfer of individualdata from a DCS to tracker nodes along parallel paths in a first timeslot.

FIG. 21 b is a plan view of another embodiment of transfer of individualdata from a DCS to tracker nodes along parallel paths in a second timeslot.

FIG. 21 c is a plan view of another embodiment of transfer of individualdata from a DCS to tracker nodes along parallel paths in a third timeslot.

FIG. 21 d is a plan view of another embodiment of transfer of individualdata from a DCS to tracker nodes along parallel paths in a fourth timeslot.

FIG. 22 is a flow chart illustrating one embodiment of a method of theinvention for wireless communication.

FIG. 23 is a flow chart illustrating another embodiment of a method ofthe invention for wireless communication.

FIG. 24 is a flow chart illustrating yet another embodiment of a methodof the invention for wireless communication.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates embodiments of the invention, in several forms, theembodiments disclosed below are not intended to be exhaustive or to beconstrued as limiting the scope of the invention to the precise formsdisclosed.

DESCRIPTION OF THE INVENTION

In accordance with the invention, one embodiment of a solar trackerwireless monitoring and tracking arrangement 20 is shown in FIG. 2 a.Arrangement 20 includes a central data control system (DCS) 22 which islocated within a matrix of rows and columns of trackers 24. In a secondembodiment of a solar tracker wireless monitoring and trackingarrangement 120 illustrated in FIG. 2 b, trackers 124 are arranged inconcentric rings surrounding a central data control system (DCS) 122.Thus, the solar plant may have trackers arranged either in a rectangulargrid or in concentric circles as shown in FIGS. 2 a-b. Two types ofcommunication that may be involved in the invention include datacollection and data communication (e.g., data transmission). In datacollection, status messages from each tracker may be sent to, andcollected by, the DCS. In data communication, query/control messages maybe transmitted from the DCS to the trackers. This query/control messagecan be unique for each tracker or can be a broadcast message that isidentical for each tracker.

With regard to data collection, various sweeping schemes of theinvention for a rectangular grid topology are illustrated in the tableof FIG. 3 and FIGS. 4 a-e. Which of the schemes is to be implemented ina particular application may depend on the arrangement of the trackers,and the total number of trackers, in the selected quadrant. FIG. 4 aillustrates a vertical sweeping scheme with horizontal collection. Eacharrow represents a transfer of data from one tracker to an adjacenttracker. Each tracker in a same row may transmit the data during a sametime slot. For example, each tracker in row 1 (i=1) may transmit to itsrespective adjacent tracker in row 2 (i=2) in the same time slot; eachtracker in row 2 (i=2) may transmit to its respective adjacent trackerin row 3 (i=3) in a same subsequent time slot, etc. After all the datain each column has been received by a respective end tracker in thecolumn (e.g., in row n), then, in a next time slot, the data may betransferred from the end tracker in column 1 (i=n, j=1) to the endtracker in column 2 (i=n, j=2). In a subsequent time slot, all the dataheld by the end tracker in column 2 (i=n, j=2) may be transferred to theend tracker in column 3 (i=n, j=3), etc., until finally all of the datain the grid has been transferred to a data collector 226 a in row n andcolumn m (i=n, j=m).

Conversely, FIG. 4 b illustrates a horizontal sweeping scheme withvertical collection. Again, each arrow represents a transfer of datafrom one tracker to an adjacent tracker. Each tracker in a same columnmay transmit the data during a same time slot. For example, each trackerin column 1 (j=1) may transmit to its respective adjacent tracker incolumn 2 (j=2) in the same time slot; each tracker in column 2 (j=2) maytransmit to its respective adjacent tracker in column 3 (j=3) in a samesubsequent time slot, etc. After all the data in each row has beenreceived by a respective end tracker in the row (e.g., in column m),then, in a next time slot, the data may be transferred from the endtracker in row 1 (i=1, j=m) to the end tracker in row 2 (i=2, j=m). In asubsequent time slot, all the data held by the end tracker in row 2(i=2, j=m) may be transferred to the end tracker in row 3 (i=3, j=m),etc., until finally all of the data in the grid has been transferred toa data collector 226 b in row n and column m (i=n, j=m).

FIGS. 4 c-e illustrate a diagonal sweeping scheme with horizontal andvertical collection. Again, each arrow represents a transfer of datafrom one tracker to an adjacent tracker. During a first time slot, asillustrated in FIG. 4 c, each tracker in an end column 1 (j=1) and/or inan end row 1 (i=1) (except for the tracker at the end of the end columnat i=n, j=1 and the tracker at the end of the end row at i=1, j=m) maytransmit data to its respective diagonally adjacent tracker.

In a second time slot illustrated in FIG. 4 d, each tracker thatreceived data in the first time slot, and that has a diagonally adjacenttracker, transfers all data held by the tracker to the diagonallyadjacent tracker. If a tracker received data in the first time slot butdoes not have a diagonally adjacent tracker, then the tracker may makeno transfer in the second time slot. In the case of a tracker in the endcolumn or the end row that does not have a diagonally adjacent tracker(i.e., the tracker at i=n, j=1 and the tracker at i=1, j=m), the trackertransmits data to the horizontally adjacent tracker or the verticallyadjacent tracker in the second time slot.

In a third time slot illustrated in FIG. 4 e, each tracker that receiveddata in the second time slot, and that has a diagonally adjacenttracker, transfers all data held by the tracker to the diagonallyadjacent tracker. If a tracker received data only diagonally but doesnot have a diagonally adjacent tracker, then the tracker may make notransfer in the third time slot. If a tracker received data horizontallyor vertically in the second time slot (i.e., the tracker at i=n, j=2 andthe tracker at i=2, j=m), then the tracker transmits data to thehorizontally adjacent tracker or the vertically adjacent tracker in thethird time slot. This process continues until all of the data has beencollected in a data collector 226 c, which is the final destination.

One embodiment of the vertical sweeping scheme is illustrated in furtherdetail in FIGS. 5 a-f, wherein data flow occurs in every time slot. Inslot 1 (FIG. 5 a), the trackers in row i=1 each transmit its data to itsrespective adjacent neighbor in row i=2. In the next slot 2 (FIG. 5 b),each tracker in row 2 transmits its own data as well as data collectedby the tracker in slot 1 to its respective adjacent neighbor in row 3,and so on. This process continues until slot i=n−1 (FIG. 5 c) whereineach of the trackers in the second to last row i=n−1 transmits its owndata as well as data collected by the tracker in slot n−2 to itsrespective adjacent neighbor in row i=n.

In slot n (FIG. 5 d), the end tracker in column j=1 (i.e., the trackerat i=n, j=1) transmits its own data as well as data collected by thetracker in slot n−1 to its adjacent neighbor in column j=2 (i.e., thetracker at i=n, j=2). In slot n+1 (FIG. 5 e), the end tracker in columnj=2 (i.e., the tracker at i=n, j=2) transmits its own data as well asdata collected by the tracker in slot n to its adjacent neighbor incolumn j=3 (i.e., the tracker at i=n, j=3), and so on. This processcontinues until slot i=n+m−2 (FIG. 5 f) wherein the end tracker in thesecond to last column j=m−1 transmits its own data as well as datacollected by the tracker in slot n+m−3 to data collector 326.

In FIGS. 4 a-c and 5 a-f, it is assumed that there are enough frequencychannels available for each tracker to simultaneously transmit in itsown designated slot. That is, each tracker node within a slot transmitsusing a non-overlapping channel. However, this is not practicallypossible when the number of tracker nodes transmitting in a slot isgreater than the number of available non-overlapping frequency channels.In this case, the trackers may still follow the same communication path,but some of the trackers may transmit in different slots. For example,if the number of columns exceeds the number of available frequencychannels in a vertical sweeping scheme, then instead of schedulingtransmission from a respective tracker in each of the columnssimultaneously, then some of the trackers may transmit in a first timeslot, and the remainder of the trackers may transmit in one or moresubsequent time slots. If there are only two frequency channelsavailable, then transmission by a respective tracker in each of columns1 and 2 may be scheduled in a first time slot, transmission by arespective tracker in each of columns 3 and 4 may be scheduled in asecond or other subsequent time slot, and so on.

In an optimization method of the invention, a given frequency may beused for transmission by more than one tracker simultaneously (e.g., ina same time slot). In order to maximize the usage of availablefrequencies, a given matrix of trackers can be divided into severalsub-matrixes which can employ sweeping while sharing at least some ofthe same frequency channels. Given a matrix of rows and columns oftrackers, and assuming a vertical sweeping scheme, two scenarios arepossible. In a first such scenario, the interference range covers all mtracker nodes in the row. That is, a receiving tracker node in an endcolumn is capable of receiving an interfering transmission from atracker node in an opposite end column. In a second such scenario, theinterference range covers x neighbor nodes given by └I/d_(c)┘, wherein Iis the interference (channel re-use) distance, d_(c) is the distance ofseparation between two adjacent columns, and m is the number of trackernodes in each row. That is, as illustrated in FIG. 6, a receivingtracker node in an end column (e.g., j=1) is capable of receiving aninterfering transmission from a tracker node in column j=x, but is notcapable of receiving an interfering transmission from a tracker node ina column that is one column farther (column j=x+1). Thus,I=(x−1)d_(c)<(m−1)d_(c).

Combining the above two scenarios, the maximum number of nodes in asingle row covered by an interference range may be given by:

$x = {\min\left( {\left\lfloor \frac{I}{d_{c}} \right\rfloor,{m - 1}} \right)}$

In other words, every (x+1)^(th) column can be scheduled to transmitsimultaneously using the same frequency. Thus, in the example of FIG. 6,a tracker node in column j=1 and a tracker node in any column numberedj=x+1 or greater may be scheduled to transmit simultaneously using thesame frequency. Similarly, a tracker node in column j=2 and a trackernode in any column numbered j=x+2 or greater may be scheduled totransmit simultaneously using the same frequency, and so on. Therefore,the problem may be reduced to scheduling only x+1 number of columns,wherein (x+1)≦m.

If the number of available non-overlapping frequency channels is greaterthan x, then the problem may be solved as described above (e.g., onlytracker nodes separated by a distance greater than the interferencedistance I may use the same frequency channel simultaneously). However,if the number of available non-overlapping frequency channels is notgreater than x, then, within a given sub-matrix, a tracker transmitternode is scheduled to transmit on a given channel only when its intendedreceiver node is out of interference range of every other transmitternode that is transmitting on the same channel. For a simpler and optimalimplementation, data collection may be started on column number f+1,(wherein f is the number of available non-overlapping channels) onlywhen the transmission in this column does not interfere with the ongoingcommunication in any other column.

In the example illustrated in FIGS. 7 a-h, the number of availablenon-overlapping channels f is assumed to be equal to (x−1). In a firsttransmission time slot, depicted in FIG. 7 a, x−1 tracker nodes in thefirst row each transmit in a respective frequency channel. That is, thenodes in positions (1, 1) through (1, x−1) each transmit in a respectivefrequency channel. Although the node at (1, x) does not transmit duringthe first time slot, the node at (1, x+1) transmits in the first timeslot in the same frequency channel as the node at (1, 1).

In a second transmission time slot, depicted in FIG. 7 b, n−1 trackernodes in the second row each transmit in the same respective frequencychannels as in the first time slot. That is, the nodes in positions(2, 1) through (2, x−1) each transmit in a respective frequency channel.Although neither the node at (1, x) nor the node at (2, x) transmitsduring the second time slot, the node at (2, x+1) transmits in thesecond time slot in the same frequency channel as the node at (2, 1).

In an (n−1)th transmission time slot, depicted in FIG. 7 c, x−1 trackernodes in the (n−1)th row each transmit in the same respective frequencychannel as in the first and second time slots. That is, the nodes inpositions (n−1, 1) through (n−1, x−1) each transmit in a respectivefrequency channel. The node at (n−1, x+1) transmits in the (n−1)th timeslot in the same frequency channel as the node at (n−1, 1). As can beseen in FIG. 7 c, the node at (2, x) is outside the interferencedistance I from the closest transmitting node at (n−1, x+1), and thusthe node at (1, x) may transmit to the node at (2, x) during the (n−1)thtransmission time slot without experiencing interference. In oneembodiment, the (1, x) node transmits in the same frequency channel asthe node at (n−1, 1) and the node at (n−1, x+1).

In an nth transmission time slot, depicted in FIG. 7 d, the horizontalsweeping along the bottom row of the matrix begins. Specifically, thetracker node at (n, 1) transmits its data, along with all other datacollected from the other nodes in column 1, to the horizontally adjacentnode (n, 2). Also, in the nth transmission time slot, the tracker nodeat (2, x) transmits its data, along with all other data collected fromnode (1, x), to the vertically adjacent node (3, x).

In an (n+1)th transmission time slot, depicted in FIG. 7 e, thehorizontal sweeping along the bottom row of the matrix continues.Specifically, the tracker node at (n, 2) transmits its data, along withall other data collected from the other nodes in column 2 and the nodeat (n, 1), to the horizontally adjacent node (n, 3).

In an (n+2)th transmission time slot, depicted in FIG. 7 f, thehorizontal sweeping along the bottom row of the matrix continues.Specifically, the tracker node at (n, 3) transmits its data, along withall other data collected from the other nodes in column 3 and the nodeat (n, 2), to the horizontally adjacent node (n, 4).

In a time slot subsequent to the (n+2)th time slot, depicted in FIG. 7g, the vertical sweeping is completed. Specifically, the tracker node at(n−1, x) transmits its data, along with all other data collected fromthe other nodes in column x, to the vertically adjacent node (n, x).

In a final time slot, depicted in FIG. 7 h, the horizontal sweepingalong the bottom row of the matrix is completed. Specifically, thetracker node at (n, x) transmits its data, along with all other datacollected from the other nodes in columns 1 through x, to the datacollector at position (n, x+1).

As described above, the node with index (1, x+1) can transmit at thesame time that nodes with indices (1, 1), (1, 2) and (1, 3) aretransmitting, even though node (1, x+1) transmits on the same frequencychannel as node (1, 1) because node (1, x+1) is beyond the interferencedistance of node (1, 1). The node with index (1, x) can transmit at thesame time that nodes with indices (n−1, 1), (n−1, 2), (n−1, 3) and (n−1,x+1) are transmitting, even though node (1, x) transmits on the samefrequency channel as nodes (n−1, 1) and (n−1, x+1) because node (1, x)is beyond the interference distance of nodes (n−1, 1) and (n−1, x+1). Inother words, data collection in column x begins when transmission bynodes in other columns on the same frequency channel are beyond theinterference distance.

In an optimization method of the invention described with reference toFIGS. 8 a-f, communication and/or collection of data occurs on a singlepath. In this embodiment, each node transmits to its r^(th) neighborinstead of its next or adjacent neighbor. In the specific exampleembodiment of FIGS. 8 a-f, each node transmits to its third neighbor(i.e., the node in a position three positions farther downstream thanthe transmitting node), if such a third neighbor exists. If such a thirdneighbor does not exist, then the transmitting node may be adjacent to,or the second neighbor of, the data collector, in which case thetransmitting node transmits directly to the data collector.

In general, each node transmits to its r^(th) neighbor, wherein r≦[R/d],and wherein R is the wireless communication range of the tracker and dis the distance of separation between neighboring trackers. An advantageof this embodiment is that, if a next neighbor node is dead, then themessage still reaches the final destination (e.g., the data collector).Another advantage of this embodiment is that there may be fewer hops tothe final destination. Yet another advantage of this embodiment is thatthere may be a reduced overall packet size. For example, if f number offrequency channels are used then the final packet size may be reduced bya factor of f. Still another advantage of this embodiment is that, ifmultiple frequencies available, then collection can be parallelized(e.g., can be performed in parallel).

FIG. 8 a illustrates a specific embodiment of data transfer along asingle path with only one non-overlapping frequency channel (f=1)available and eight trackers (n=8) in the path. With only onenon-overlapping frequency channel available, each of the seventransmissions (which are each indicated by a respective arrow) occurs ina separate time slot. The only constraints in the order of transmissionmay be that transmission 802 from the third node down to the sixth nodedown occurs before transmission 804 from the sixth node down to thefinal destination. Thus, transmission 804 may include the contents oftransmission 802. Similarly, transmission 806 from the first node to thefourth node down occurs before transmission 808 from the fourth nodedown to the seventh node down, and transmission 808 from the fourth nodedown to the seventh node down occurs before transmission 810 from theseventh node down to the final destination. Thus, transmission 808 mayinclude the contents of transmission 806, and transmission 810 mayinclude the contents of transmission 808. Further, transmission 812 fromthe second node to the fifth node down occurs before transmission 814from the fifth node down to the eighth node down. Thus, transmission 814may include the contents of transmission 812.

FIG. 8 b illustrates another specific embodiment of data transfer alonga single path with only one non-overlapping frequency channel (f=1)available and nine trackers (n=9) in the path. With only onenon-overlapping frequency channel available, each of the eighttransmissions (which are each indicated by a respective arrow) occurs ina separate time slot. The only constraints in the order of transmissionmay be that transmission 816 from the first node to the fourth node downoccurs before transmission 818 from the fourth node down to the seventhnode down, and transmission 818 from the fourth node down to the seventhnode down occurs before transmission 820 from the seventh node down tothe final destination. Thus, transmission 818 may include the contentsof transmission 816, and transmission 820 may include the contents oftransmission 818. Similarly, transmission 822 from the second node tothe fifth node down occurs before transmission 824 from the fifth nodedown to the eighth node down, and transmission 824 from the fifth nodedown to the eighth node down occurs before transmission 826 from theeighth node down to the final destination. Thus, transmission 824 mayinclude the contents of transmission 822, and transmission 826 mayinclude the contents of transmission 824. Further, transmission 828 fromthe third node to the sixth node down occurs before transmission 830from the sixth node down to the final destination. Thus, transmission830 may include the contents of transmission 828.

FIG. 8 c illustrates yet another specific embodiment of data transferalong a single path with two non-overlapping frequency channels (f=2)available and eight trackers (n=8) in the path. Transmission 832 fromthe first node to the fourth node occurs during the same time slot astransmission 834 from the second node to the fifth node. Aftertransmissions 832, 834, transmission 836 from the third node to thesixth node occurs during the same time slot as transmission 838 from thefourth node to the seventh node. Subsequent to transmissions 836, 838,transmission 840, 842 and 844 to the final destination from the fifth,sixth and seventh nodes, respectively, may occur in any order in time.Thus, transmission 844 may include the contents of transmission 838,which may include the contents of transmission 832; transmission 842 mayinclude the contents of transmission 836; and transmission 840 mayinclude the contents of transmission 834.

FIG. 8 d illustrates still another specific embodiment of data transferalong a single path with two non-overlapping frequency channels (f=2)available and nine trackers (n=9) in the path. Transmission 846 from thefirst node to the fourth node occurs during the same time slot astransmission 848 from the second node to the fifth node. Aftertransmissions 846, 848, transmission 850 from the third node to thesixth node occurs during the same time slot as transmission 852 from thefourth node to the seventh node. After transmissions 850, 852,transmission 854 from the fifth node to the eighth node occurs duringthe same time slot as transmission 856 from the sixth node to the finaldestination. Subsequent to transmissions 850, 852, transmission 858 fromthe seventh node down to the final destination may occur; and subsequentto transmissions 854, 856, transmission 860 from the eighth node down tothe final destination may occur. Thus, transmission 860 may include thecontents of transmission 854, which may include the contents oftransmission 848; transmission 858 may include the contents oftransmission 852, which may include the contents of transmission 846;and transmission 856 may include the contents of transmission 850.

FIG. 8 e illustrates a further specific embodiment of data transferalong a single path with three non-overlapping frequency channels (f=3)available and eight trackers (n=8) in the path. Transmission 862 fromthe first node to the fourth node occurs during the same time slot astransmission 864 from the second node to the fifth node and transmission866 from the third node to the sixth node. After transmissions 862, 864,866, transmission 868 from the fourth node to the seventh node occursduring the same time slot as transmission 870 from the fifth node to thefinal destination. Subsequent to transmissions 862, 864, 866,transmission 872 from the sixth node down to the final destination mayoccur. Subsequent to transmissions 868, 870, transmission 874 from theseventh node down to the final destination may occur. Thus, transmission874 may include the contents of transmission 868, which may include thecontents of transmission 862; transmission 872 may include the contentsof transmission 866; and transmission 870 may include the contents oftransmission 864.

FIG. 8 f illustrates another specific embodiment of data transfer alonga single path with three non-overlapping frequency channels (f=3)available and nine trackers (n=9) in the path. Transmission 876 from thefirst node to the fourth node occurs during the same time slot astransmission 878 from the second node to the fifth node and transmission880 from the third node to the sixth node. After transmissions 876, 878,880, transmission 882 from the fourth node to the seventh node occursduring the same time slot as transmission 884 from the fifth node to theeighth node and transmission 886 from the sixth node to the finaldestination. After transmissions 882, 884, 886, transmission 888 fromthe seventh node to the final destination and transmission 890 from theeighth node to the final destination occur in no particular order inseparate time slots. Thus, transmission 890 may include the contents oftransmission 884, which may include the contents of transmission 878;transmission 888 may include the contents of transmission 882, which mayinclude the contents of transmission 876; and transmission 886 mayinclude the contents of transmission 880.

In another embodiment, the invention provides data collection in theform of sweeping schemes for circular grid topology. These schemes mayinvolve the use of a circular geometry for achieving robust datacollection. Two example embodiments are illustrated in FIGS. 9 a-k andFIGS. 10 a-g, respectively. In the embodiment of FIGS. 9 a-k, data flowson concentric circle segments between trackers 924 until reaching theends of the segments, and then the data flows radially toward thecenter, i.e., toward central DCS 922. In the embodiment of FIGS. 10 a-g,in contrast, data flows only radially towards the center. Again by usingmultiple frequencies, data flow in different sectors/circles may bescheduled simultaneously. Further, the whole topology can be dividedinto multiple sectors, and different sweeping schemes can be employed inthe different sectors. Further still, different groups of frequencychannels can be used for different sectors. However, the same group offrequency channels can be used in two sectors when the two sectors areoutside of the interference range from each other.

In the example embodiment illustrated in FIGS. 9 a-k, the circulartopology is divided into six pie-shaped sectors 902 a-f. With regard toonly one sector 902 a, the number of available non-overlapping channelsf is assumed to be at least six. That is, in a first transmission timeslot, depicted in FIG. 9 a, the six tracker nodes arranged along aradial wall 904 a of sector 902 a each transmit in a respectivefrequency channel. Each of the six tracker nodes transmits to arespective one of six concentrically-adjacent nodes. Thus, in the firsttransmission time slot depicted in FIG. 9 a, concentric sweeping acrosssector 902 a begins.

The six non-overlapping channels used in sector 902 a may also be usedin sector 902 d, assuming that sectors 902 a and 902 d are outside ofeach other's interference range. In order to maximize the distancebetween nodes transmitting with a same frequency, a radially outermosttracker 906 a of sector 902 a may transmit at the same frequency as aradially innermost tracker 906 b of sector 902 d. Further, a radiallysecond outermost tracker 906 c of sector 902 a may transmit at the samefrequency as a radially second innermost tracker 906 d of sector 902 d,and so on on down the line such that a radially innermost tracker 906 eof sector 902 a may transmit at the same frequency as a radiallyoutermost tracker 906 f of sector 902 d.

Maximizing the distance between sectors using the same frequencychannels, opposing sectors 902 b and 902 e may transmit using the sameset of frequency channels. Lastly, opposing sectors 902 c and 902 f mayalso transmit using the same set of frequency channels.

In a second transmission time slot, depicted in FIG. 9 b, the concentricsweeping across sector 902 a continues. Specifically, the five trackernodes that received transmissions in the first transmission time slotbut that are not adjacent to radial wall 904 b each transmit in arespective frequency channel. Each of the five tracker nodes transmitsits data, along with all other data collected from the other nodes inthe first transmission time slot, to a respective one of fiveconcentrically-adjacent nodes.

In a third transmission time slot, depicted in FIG. 9 c, the concentricsweeping across sector 902 a continues. Specifically, the four trackernodes that received transmissions in the second transmission time slotbut that are not adjacent to radial wall 904 b each transmit in arespective frequency channel. Each of the four tracker nodes transmitsits data, along with all other data collected from the other nodes inthe second transmission time slot, to a respective one of fourconcentrically-adjacent nodes.

In a fourth transmission time slot, depicted in FIG. 9 d, the concentricsweeping across sector 902 a continues. Specifically, the three trackernodes that received transmissions in the third transmission time slotbut that are not adjacent to radial wall 904 b each transmit in arespective frequency channel. Each of the three tracker nodes transmitsits data, along with all other data collected from the other nodes inthe third transmission time slot, to a respective one of threeconcentrically-adjacent nodes.

In a fifth transmission time slot, depicted in FIG. 9 e, the concentricsweeping across sector 902 a is completed. Specifically, the two trackernodes that received transmissions in the fourth transmission time slotbut that are not adjacent to radial wall 904 b each transmit in arespective frequency channel. Each of the two tracker nodes transmitsits data, along with all other data collected from the other nodes inthe fourth transmission time slot, to a respective one of twoconcentrically-adjacent nodes.

In a sixth transmission time slot, depicted in FIG. 9 f, the radialsweeping toward central DCS 922 begins. Specifically, the radiallyoutermost tracker node 906 g transmits its data, along with all otherdata collected from the other nodes in the fifth transmission time slot,to a radially-adjacent tracker node 906 h.

In a seventh transmission time slot, depicted in FIG. 9 g, the radialsweeping toward central DCS 922 continues. Specifically, tracker node906 h transmits its data, along with all other data collected from theother nodes in the sixth transmission time slot, to a radially-adjacenttracker node 906 i.

In an eighth transmission time slot, depicted in FIG. 9 h, the radialsweeping toward central DCS 922 continues. Specifically, tracker node906 i transmits its data, along with all other data collected from theother nodes in the seventh transmission time slot, to aradially-adjacent tracker node 906 j.

In a ninth transmission time slot, depicted in FIG. 9 i, the radialsweeping toward central DCS 922 continues. Specifically, tracker node906 j transmits its data, along with all other data collected from theother nodes in the eighth transmission time slot, to a radially-adjacenttracker node 906 k.

In a tenth transmission time slot, depicted in FIG. 9 j, the radialsweeping toward central DCS 922 continues. Specifically, tracker node906 k transmits its data, along with all other data collected from theother nodes in the ninth transmission time slot, to a radially-adjacenttracker node 906 l.

In a final time slot, depicted in FIG. 9 k, the radial sweeping towardcentral DCS 922 is completed. Specifically, tracker node 906 l transmitsits data, along with all other data collected from the other nodes inthe tenth transmission time slot, to central DCS 922.

In the example embodiment illustrated in FIGS. 10 a-g, the circulartopology is divided into six pie-shaped sectors 1002 a-f. With regard toonly one sector 1002 a, the number of available non-overlapping channelsf is assumed to be at least six. That is, in a first transmission timeslot, depicted in FIG. 10 a, the six radially outermost tracker nodeseach transmit in a respective frequency channel. Each of the six trackernodes transmits to a respective one of six radially-adjacent nodes.Thus, in the first transmission time slot depicted in FIG. 10 a, radialsweeping towards central DCS 1022 begins.

The six non-overlapping channels used in sector 1002 a may also be usedin sector 1002 b, assuming that sectors 1002 a and 1002 b are outside ofeach other's interference range. In order to maximize the distancebetween nodes transmitting with a same frequency, a counterclockwisemosttracker 1006 a of sector 1002 a may transmit at the same frequency as acounterclockwisemost tracker 1006 b of sector 1002 b. Further, a secondcounterclockwisemost tracker 1006 c of sector 1002 a may transmit at thesame frequency as a second counterclockwisemost tracker 1006 d of sector1002 b, and so on on down the line such that a clockwisemost tracker1006 e of sector 1002 a may transmit at the same frequency as aclockwisemost tracker 1006 f of sector 1002 b.

The frequency channel scheme of sectors 1002 a-b may be replicated insectors 1002 c-f, assuming that the radially outermost width of each ofthe sectors is large enough to avoid interference between trackerstransmitting on same frequency channels. As the transmissions convergetowards central DCS 1022, however, the distances between simultaneouslytransmitting trackers may become small enough that interference ispossible. At that point, trackers transmitting from correspondingpositions within the sectors may transmit with different frequencies.Alternatively, the trackers may take turns transmitting such that theydo not transmit at the same time on the same frequency.

In another embodiment, however, the relative frequency schemes ofsectors 1002 a-f is similar to that described above for sectors 902 a-f.That is, the six non-overlapping channels used in sector 1002 a may alsobe used in opposing sector 1002 d, assuming that sectors 1002 a and 1002d are outside of each other's interference range. Maximizing thedistance between sectors using the same frequency channels, opposingsectors 1002 b and 1002 e may transmit using the same set of frequencychannels. Lastly, opposing sectors 1002 c and 1002 f may also transmitusing the same set of frequency channels.

In a second transmission time slot, depicted in FIG. 10 b, the radialsweeping toward the center continues. Specifically, the five trackernodes that received transmissions in the first transmission time slotbut that are not adjacent to radial wall 1004 b each transmit in arespective frequency channel. Each of the five tracker nodes transmitsits data, along with all other data collected from the other nodes inthe first transmission time slot, to a respective one of fiveradially-adjacent nodes.

In a third transmission time slot, depicted in FIG. 10 c, the radialsweeping toward the center continues. Specifically, the four trackernodes that received transmissions in the second transmission time slotbut that are not adjacent to radial wall 1004 b each transmit in arespective frequency channel. Each of the four tracker nodes transmitsits data, along with all other data collected from the other nodes inthe second transmission time slot, to a respective one of fourradially-adjacent nodes. Also, a clockwisemost tracker that received atransmission in the first transmission time slot transmits its data,along with all other data collected from the other nodes in the firsttransmission time slot, to a radially-adjacent node that is adjacent toradial wall 1004 b.

In a fourth transmission time slot, depicted in FIG. 10 d, the radialsweeping toward the center continues. Specifically, the three trackernodes that received transmissions in the third transmission time slotbut that are not adjacent to radial wall 1004 b each transmit in arespective frequency channel. Each of the three tracker nodes transmitsits data, along with all other data collected from the other nodes inthe third transmission time slot, to a respective one of threeradially-adjacent nodes. Also, the remaining tracker that received atransmission in the third transmission time slot transmits its data,along with all other data collected from the other nodes in the thirdtransmission time slot, to a radially-adjacent node that is adjacent toradial wall 1004 b.

In a fifth transmission time slot, depicted in FIG. 10 e, the radialsweeping toward the center continues. Specifically, the two trackernodes that received transmissions in the fourth transmission time slotbut that are not adjacent to radial wall 1004 b each transmit in arespective frequency channel. Each of the two tracker nodes transmitsits data, along with all other data collected from the other nodes inthe fourth transmission time slot, to a respective one of tworadially-adjacent nodes. Also, the remaining tracker that received atransmission in the fourth transmission time slot transmits its data,along with all other data collected from the other nodes in the fourthtransmission time slot, to a radially-adjacent node that is adjacent toradial wall 1004 b.

In a sixth transmission time slot, depicted in FIG. 10 f, the radialsweeping toward central DCS 1022 continues. Specifically, the trackernode that received transmissions in the fifth transmission time slot butthat is not adjacent to radial wall 1004 b transmits to central DCS1022. The tracker node transmits its data, along with all other datacollected from the other nodes in the fifth transmission time slot, tocentral DCS 1022. Also, the remaining tracker that received atransmission in the fifth transmission time slot transmits its data,along with all other data collected from the other nodes in the fifthtransmission time slot, to a radially-adjacent node that is adjacent toradial wall 1004 b.

In a final time slot, depicted in FIG. 10 g, the radial sweeping towardcentral DCS 1022 is completed. Specifically, the clockwisemost trackernode that is radially-adjacent to central DCS 1022 transmits its data,along with all other data collected from the other nodes in the sixthtransmission time slot, to central DCS 1022.

In another embodiment, the invention provides a random slotted scheme ofdata collection that may be used with any tracker topology. Given theconnectivity graph between the trackers and the main computer,transmissions by the trackers can be scheduled with no collision usingsome fixed number of frequency channels such that all trackers can sendtheir data packet to the main computer as fast as possible. An exampleof such a scheme is illustrated in FIGS. 11 a-f. There are no topologyconstraints for such a scheme and the scheme can be used for bothrectangular and circular grid topologies.

In the example embodiment illustrated in FIGS. 11 a-f, the data flowsgenerally from outer trackers toward a centralized DCS 1122, perhapsbeing relayed by one or more other trackers along the way. However,there is no requirement that the DCS be centralized. Rather, the DCS maybe disposed anywhere along the outskirts of the distribution of thetrackers.

Although different transmitting trackers may transmit on the samefrequency channel simultaneously, a minimum difference between a firstdistance between a receiving tracker and one of the transmittingtrackers and a second distance between the receiving tracker and anothertransmitting tracker using the same frequency channel may be called for.Thus, a difference in received signal strengths between two signalsbeing simultaneously transmitted on a same frequency channel may begreat enough that the receiving node can easily distinguish between thetwo signals, and no interference occurs in practical terms.

In a first transmission time slot, depicted in FIG. 11 a, five trackernodes 1106 a-e each transmit in a same first frequency channel; fourtracker nodes 1106 f-i each transmit in a same second frequency channel;and two tracker nodes 1106 j-k each transmit in a same third frequencychannel. As shown in each of FIGS. 11 a-f, no tracker node bothtransmits and receives in a same transmission time slot.

In a second transmission time slot, depicted in FIG. 11 b, three trackernodes 1106 l-n each transmit in the first frequency channel; one trackernode 1106 p transmits in the second frequency channel; and one trackernode 1106 q transmits in the third frequency channel. As can be seen ina comparison of FIGS. 11 a-b, each of the tracker nodes 1106 l-q thattransmits in the second time slot depicted FIG. 11 b also receives atransmission in the first time slot depicted in FIG. 11 a.

In a third transmission time slot, depicted in FIG. 11 c, two trackernodes 1106 r-s each transmit in the first frequency channel; and twotracker nodes 1106 t-u each transmit in the second frequency channel. Ascan be seen in a comparison of FIGS. 11 a-c, each of the tracker nodes1106 r-u that transmits in the third time slot depicted FIG. 11 c alsoreceives a transmission in the first time slot depicted in FIG. 11 aand/or the second time slot depicted in FIG. 11 b.

In a fourth transmission time slot, depicted in FIG. 11 d, two trackernodes 1106 v-w each transmit in the first frequency channel. As can beseen in a comparison of FIGS. 11 a-d, each of the tracker nodes 1106 v-wthat transmits in the fourth time slot depicted FIG. 11 d also receivesa transmission in the first time slot depicted in FIG. 11 a and thethird time slot depicted in FIG. 11 c.

In a fifth transmission time slot, depicted in FIG. 11 e, a tracker node1106 x transmits in the first frequency channel. As can be seen in acomparison of FIGS. 11 a-e, tracker node 1106 x does not receive atransmission in any of the five time slots.

In a sixth and final transmission time slot, depicted in FIG. 11 f, atracker node 1106 y transmits in the first frequency channel to DCS1122. As can be seen in a comparison of FIGS. 11 a-f, tracker node 1106y receives a transmission in each of the second, third, fourth and fifthtime slots.

In a specific embodiment, in order to increase the efficiency andreliability of the base scheme, the time duration of the transmissiontime slots may be variable. For example, instead of the time durationsof the transmission time slots being fixed, the time duration of atransmission time slot can vary depending on the maximum, average orminimum size of all packet data transmissions scheduled in that slot.

In another embodiment, multiple collection schedules may be utilized. Aseach node can send data to two or more different nodes in the network,multiple schedules can be overlapped together, as shown in FIGS. 12 a-l.

In a first transmission time slot, depicted in FIG. 12 a, seven trackernodes 1206 a-g each transmit in a same first frequency channel; fourtracker nodes 1206 h-k each transmit in a same second frequency channel;and three tracker nodes 1206 l-n each transmit in a same third frequencychannel. In this first transmission time slot, all transmissions areaccording to a first schedule. As shown in each of FIGS. 12 a-l, notracker node both transmits and receives in a same transmission timeslot.

In a second transmission time slot, depicted in FIG. 12 b, six trackernodes 1206 p-u each transmit in the first frequency channel; fourtracker nodes 1206 v-y transmit in the second frequency channel; andthree tracker nodes 1206 z and 1206 aa-bb transmit in the thirdfrequency channel. All of the above-described transmissions in thesecond transmission time slot are according to the first schedule. Inaddition, according to a second schedule depicted by dashed arrows inFIGS. 12 b-l, tracker nodes 1206 b and 1206 d each again transmit in thesecond transmission time slot, just as they transmitted in the firsttransmission time slot, but this time transmit to different trackernodes than in the first transmission time slot. However, they maytransmit the same information in the second transmission time slot as inthe first transmission time slot. Tracker nodes 1206 b and 1206 d eachtransmit in the third frequency channel according to the secondschedule, rather than in the first frequency channel according to thefirst schedule.

In a third transmission time slot, depicted in FIG. 12 c, four trackernodes 1206 cc-ff each transmit in the first frequency channel; threetracker nodes 1206 gg-ii transmit in the second frequency channel; andone tracker node 1206 jj transmits in the third frequency channel. Allof the above-described transmissions in the third transmission time slotare according to the first schedule. In addition, according to thesecond schedule, tracker nodes 1206 c, 1206 p, 1206 a, 1206 j, 1206 fand 1206 t each again transmit in the third transmission time slot, justas they transmitted in the first or second transmission time slots, butthis time transmit to different tracker nodes than in the first orsecond transmission time slots. However, they may transmit the sameinformation in the third transmission time slot as in the first orsecond transmission time slots. According to the second schedule,tracker node 1206 c transmits in the first frequency channel; trackernode 1206 p transmits in the second frequency channel; and tracker nodes1206 a, 1206 j, 1206 f and 1206 t each transmit in the third frequencychannel.

In a fourth transmission time slot, depicted in FIG. 12 d, two trackernodes 1206 kk-ll each transmit in the first frequency channel; twotracker nodes 1206 mm-nn transmit in the second frequency channel; andtwo tracker nodes 1206 oo-pp transmit in the third frequency channel.All of the above-described transmissions in the fourth transmission timeslot are according to the first schedule. In addition, according to thesecond schedule, tracker nodes 1206 i, 1206 r, 1206 k, 1206 h, 1206 ii,1206 dd and 1206 x each again transmit in the fourth transmission timeslot, just as they transmitted in the first, second or thirdtransmission time slots, but this time transmit to different trackernodes than in the first, second or third transmission time slots.However, they may transmit the same information in the fourthtransmission time slot as in the first, second or third transmissiontime slots. According to the second schedule, tracker nodes 1206 i, 1206r and 1206 k transmit in the first frequency channel; tracker nodes 1206h and 1206 ii transmit in the second frequency channel; and trackernodes 1206 dd and 1206 x each transmit in the third frequency channel.

In a fifth transmission time slot, depicted in FIG. 12 e, two trackernodes 1206 qq-rr each transmit in the first frequency channel; onetracker node 1206 ss transmits in the second frequency channel; and onetracker node 1206 tt transmits in the third frequency channel. All ofthe above-described transmissions in the fifth transmission time slotare according to the first schedule. In addition, according to thesecond schedule, tracker nodes 1206 l, 1206 g, 1206 ee, 1206 y, 1206 nand 1206 u each again transmit in the fifth transmission time slot, justas they transmitted in the first, second or third transmission timeslots, but this time transmit to different tracker nodes than in thefirst, second or third transmission time slots. However, they maytransmit the same information in the fifth transmission time slot as inthe first, second or third transmission time slots. According to thesecond schedule, tracker nodes 1206 l and 1206 g transmit in the firstfrequency channel; tracker nodes 1206 ee, 1206 y and 1206 n transmit inthe second frequency channel; and tracker nodes 1206 u transmits in thethird frequency channel.

In a sixth transmission time slot, depicted in FIG. 12 f, one trackernode 1206 uu transmits in the first frequency channel; and one trackernode 1206 vv transmits in the second frequency channel. The twoabove-described transmissions in the sixth transmission time slot areaccording to the first schedule. In addition, according to the secondschedule, tracker nodes 1206 cc, 1206 w, 1206 ff, 1206 jj, 1206 m, 1206v, 1206 hh and 1206 s each again transmit in the sixth transmission timeslot, just as they transmitted in the second or third transmission timeslots, but this time transmit to different tracker nodes than in thesecond or third transmission time slots. However, they may transmit thesame information in the sixth transmission time slot as in the second orthird transmission time slots. According to the second schedule, trackernodes 1206 cc, 1206 w and 1206 ff each transmit in the first frequencychannel; tracker nodes 1206 jj and 1206 m each transmit in the secondfrequency channel; and tracker nodes 1206 v, 1206 hh and 1206 s eachtransmit in the third frequency channel.

In a seventh transmission time slot, depicted in FIG. 12 g, one trackernode 1206 ww transmits in the first frequency channel according to thefirst schedule. In addition, according to the second schedule, trackernodes 1206 kk, 1206 q, 1206 aa, 1206 bb, 1206 oo and 1206 nn each againtransmit in the seventh transmission time slot, just as they transmittedin the second or third transmission time slots, but this time transmitto different tracker nodes than in the second or third transmission timeslots. However, they may transmit the same information in the seventhtransmission time slot as in the second or third transmission timeslots. According to the second schedule, tracker node 1206 kk transmitsin the first frequency channel; tracker nodes 1206 q, 1206 aa and 1206bb each transmit in the second frequency channel; and tracker nodes 1206oo and 1206 nn each transmit in the third frequency channel.

In an eighth transmission time slot, depicted in FIG. 12 h, one trackernode 1206 e again transmits in the first frequency channel to DCS 1222according to the first schedule, just as it transmitted in the firsttransmission time slot, but this time transmit to a different trackernode than in the first transmission time slot. In addition, according tothe second schedule, tracker nodes 1206 gg, 1206 n, 1206 ll and 1206 sseach again transmit in the eighth transmission time slot, just as theytransmitted in the third, fourth or fifth transmission time slots, butthis time transmit to different tracker nodes than in the third, fourthor fifth transmission time slots. However, they may transmit the sameinformation in the eighth transmission time slot as in the third, fourthor fifth transmission time slots. According to the second schedule,tracker nodes 1206 gg, 1206 n and 1206 ll each transmit in the secondfrequency channel; and tracker node 1206 ss transmits in the thirdfrequency channel.

In a ninth transmission time slot, depicted in FIG. 12 i, none of thetracker nodes transmit according to the first schedule. However,according to the second schedule, tracker nodes 1206 z, 1206 uu, 1206 mmand 1206 pp each again transmit in the ninth transmission time slot,just as they transmitted in the second, fourth or sixth transmissiontime slots. Tracker node 1206 pp again transmits to DCS 1222, just as itdid in the fourth transmission time slot. But this time tracker nodes1206 z, 1206 uu and 1206 mm transmit to different tracker nodes than inthe second, fourth or sixth transmission time slots. However, trackernodes 1206 z, 1206 uu, 1206 mm and/or 1206 pp may transmit the sameinformation in the ninth transmission time slot as in the second, fourthor sixth transmission time slots. According to the second schedule,tracker nodes 1206 z, 1206 uu each transmit in the first frequencychannel; tracker node 1206 mm transmits in the second frequency channel;and tracker node 1206 pp transmits in the third frequency channel.

In a tenth transmission time slot, depicted in FIG. 12 j, none of thetracker nodes transmit according to the first schedule. However,according to the second schedule, tracker nodes 1206 ww and 1206 tt eachagain transmit in the tenth transmission time slot, just as theytransmitted in the fifth or seventh transmission time slots, but thistime transmit to different tracker nodes than in the fifth or seventhtransmission time slots. However, tracker nodes 1206 ww and 1206 tt maytransmit the same information in the tenth transmission time slot as inthe fifth or seventh transmission time slots. According to the secondschedule, tracker node 1206 ww transmits in the first frequency channel;and tracker node 1206 tt transmits in the second frequency channel.

In an eleventh transmission time slot, depicted in FIG. 12 k, none ofthe tracker nodes transmit according to the first schedule. However,according to the second schedule, tracker nodes 1206 qq again transmitsin the eleventh transmission time slot, just as it transmitted in thefifth transmission time slot, but this time transmits to a differenttracker node than in the fifth transmission time slot. However, trackernode 1206 qq may transmit the same information in the eleventhtransmission time slot as in the fifth transmission time slot. Accordingto the second schedule, tracker node 1206 qq transmits in the firstfrequency channel.

In a final transmission time slot, depicted in FIG. 12 l, none of thetracker nodes transmit according to the first schedule. However,according to the second schedule, tracker node 1206 vv again transmitsin the final transmission time slot, just as it transmitted in the sixthtransmission time slot, but this time transmits to DCS 1222 rather thanto a tracker node as node 1206 vv did in the sixth transmission timeslot. However, tracker node 1206 vv may transmit the same information inthe final transmission time slot as in the sixth transmission time slot.According to the second schedule, tracker node 1206 vv transmits in thefirst frequency channel.

An advantage of such a multiple collection schedule, random slottedscheme is that it is faster than other methods, and thus moretime-efficient. Another advantage is that the scheme may keep all nodesbusy. Links unused in the first round/time slot may be used insubsequent rounds/time slots. Yet another advantage is that the schememay be more reliable and robust. The schedule may be computed such thateach node receives the message from different sources in differentrounds/time slots. A further advantage of the scheme is that it is easyto implement. That is, nodes may simply follow a pre-computed schedule.U.S. Pat. No. 7,738,455 (serial application Ser. No. 11/488,380) toKeshavarzian et al. discloses details on how such a scheme may beimplemented, and is hereby incorporated by reference herein in itsentirety.

In another embodiment depicted in FIG. 13, a hierarchical scheme of datacollection may be performed in conjunction with any topology. Agroup/grid of trackers can also form individual clusters, there being amatrix of eight clusters including two rows of four clusters eachillustrated in FIG. 13. Each cluster is made up of a matrix of nineelements including three rows of three elements each. The center elementin each matrix is a cluster head, and the remaining eight elements inthe matrix are all normal trackers. Each cluster head may be a trackeror a dedicated wireless node. All trackers may send their data to theircluster head which may then aggregate the data and send it to theDCS/Master data collector. As shown in FIG. 13, this DCS/Master datacollector may be disposed in the middle of the matrix of clusters, e.g.,between the first and second rows of clusters, and between the secondand third rows of clusters. If the distance between the cluster head andthe master collector is more than the wireless communication range, thenthe cluster head can use any other cluster head along the path as anintermediate hop to communicate with the master controller. For example,if DCS 1322 is beyond the wireless communication range of cluster head1392, then cluster head 1392 may instead transmit to cluster head 1394,and cluster head 1394 may relay the message to DCS 1322.

For better performance, frequencies may be reused, but adjacent clusterscan communicate on different frequency channels. However, clustersoutside the interference range (e.g., the channel re-use distance) ofeach other may operate on same frequency channel. As illustrated in FIG.13, clusters 1301 and 1303 are distanced from each other by at least thechannel re-use distance. Thus, clusters 1301 and 1303 may both transmitwithin frequency channel 1. Similarly, clusters 1305 and 1307 may bothtransmit within frequency channel 2; clusters 1309 and 1311 may bothtransmit within a third frequency channel; and clusters 1313 and 1315may both transmit within a fourth frequency channel.

In another embodiment, multiple radio antennas and/or directionalantennas may be employed in the embodiment of FIG. 13. For example, thecluster head nodes can employ additional radio or directional antennasto communicate with the master node DCS directly without using anintermediate cluster head as a relay node. The antennas may be calledfor in transmitting to the DCS because the distance between a clusterhead and the master collector DCS may be many times greater than thedistance between the cluster head and the trackers in its same cluster.

In another embodiment depicted in FIG. 14, a divide and conquer schemeof data collection may be performed in conjunction with any topology.The whole rectangular grid or matrix of tracker nodes can be dividedinto multiple sections. In the specific embodiment of FIG. 14, the gridis divided into four equally sized quadrants having equal numbers oftracker nodes. In each quadrant, respective data collection schemes maybe implemented simultaneously, thereby reducing the overall datacollection time by about 75 percent. The data collection schemes in eachquadrant may be the same or different. Further, each quadrant can alsoemploy different communication schemes, different frequency channels,etc., so as to improve the overall communication.

In other embodiments depicted in FIGS. 15-16, a communication path maybe divided into sectors. For example, a given path, including allparallel scheduled paths, may be divided into multiple sectors whereinthe multiple sectors can be scheduled simultaneously. This may result insmaller packets and a faster response time, especially in cases in whichdata is aggregated at every step. FIGS. 15 a-g illustrate such a schemewherein the number of bytes of overhead for every packet is representedby the letter “o” and the number of bytes of data to be sent by everynode on the path is represented by the letter “a”. The top half of thediagram in each of FIGS. 15 a-g represents a data collection pathwithout sectoring; and the bottom half of the diagram in each of FIGS.15 a-g represents a data collection path with sectoring, such as shownin FIG. 14. In FIG. 15 a it can be seen that the communication pathincludes eleven tracker nodes 1506 and one DCS 1522 on the right-handend of the diagram. In the first time slot depicted in FIG. 15 b it maybe observed that, with sectoring, two nodes 1506 a-b in both sectorstransmit simultaneously and total time consumed is still the same. Thatis, the time needed to transmit ‘o+a’ (1+1=2) bytes is the same.Generally in FIGS. 15 a-g, communication on channel 1 is represented bya solid arced line between nodes 1506; and communication on channel 2 isrepresented by a dashed arced line between nodes 1506.

FIG. 15 c depicts both the first and second time slots. The total timeneeded to transmit ‘o+a’ bytes remains same in the conventional andsectored communication paths. That is, in both methods, two bytes ofoverhead and three bytes of data need to be transmitted.

FIG. 15 d depicts the first through third time slots. The total timeneeded to transmit ‘o+a’ bytes remains same in the conventional andsectored communication paths. That is, in both methods, three bytes ofoverhead and six bytes of data need to be transmitted.

FIG. 15 e depicts the first through fourth time slots. In the fourthtime slot, the benefits of sectoring begin to materialize. It should benoted that trackers in sector two have no data to transmit. Hence fromthe fourth time slot onwards the trackers in sector two relay data ofonly nodes from sector one. Therefore, the duration of the fourth timeslot required by the sectored scheme may be less than the duration ofthe fourth time slot in the non-sectored scheme. Thus, the overall timeneeded to transmit four bytes of overhead and ten bytes of data in thenon-sectored scheme is greater than the time needed to transmit fourbytes of overhead and nine bytes of data in the sectored scheme.

FIG. 15 f depicts the first through fifth time slots. The duration ofthe fifth time slot required by the sectored scheme may be less than theduration of the fifth time slot in the non-sectored scheme. Moreover,the overall time needed to transmit five bytes of overhead and fifteenbytes of data in the non-sectored scheme is greater than the time neededto transmit five bytes of overhead and twelve bytes of data in thesectored scheme.

FIG. 15 g depicts the first through sixth time slots. The duration ofthe sixth time slot required by the sectored scheme may be less than theduration of the sixth time slot in the non-sectored scheme. Moreover,the overall time needed to transmit six bytes of overhead and twenty-onebytes of data in the non-sectored scheme is greater than the time neededto transmit six bytes of overhead and fifteen bytes of data in thesectored scheme. That is, the overall communication time for thenon-sectored scheme may include transmission time for ‘6o+21a’ bytes ofdata while for the sectored scheme the overall communication time mayrequire transmission time for only ‘6o+15a’ bytes of data. Thus, thebenefits of sectoring are clearly demonstrated. One restriction on thesectored scheme may be that the communications in the separate sectorsnot interfere with each other. Also, a given path can be divided intomultiple sectors.

FIGS. 16 a-f illustrate another embodiment including sectoring in whichtwo adjacent paths are divided into multiple sectors. The top half ofthe diagram in each of FIGS. 16 a-f represents a first data collectionpath divided in three sectors; and the bottom half of the diagram ineach of FIGS. 16 a-f represents a second, adjacent data collection pathalso divided in three sectors. Generally in FIGS. 16 a-f, communicationon channel 1 is represented by a solid arced line between nodes;communication on channel 2 is represented by a dashed arced line betweennodes; communication on channel 3 is represented by an arced linebetween nodes including both dashes and dots; and communication onchannel 4 is represented by a dotted arced line between nodes. Further,in each of FIGS. 16 a-f, a tracker node whose data is being received, orhas already been received, by the collector DCS at the right-hand end ofthe path is depicted by a black circle rather than a grey circle.

In the first step, depicted in FIG. 16 a, all transmissions in sector 1in both paths may occur in the same first time slot; all transmissionsin sector 2 in both paths may occur in the same second time slot; andall transmissions in sector 3 in both paths may occur in the same thirdtime slot. Similarly, in the second step, depicted in FIG. 16 b, alltransmissions from sector 1 in both paths may occur in the same fourthtime slot; all transmissions from sector 2 in both paths may occur inthe same fifth time slot; and all transmissions from sector 3 in bothpaths may occur in the same sixth time slot. Similarly, in the thirdstep, depicted in FIG. 16 c, all transmissions from sector 2 in bothpaths may occur in the same seventh time slot; and all transmissionsfrom sector 3 in both paths may occur in the same eighth time slot.Similarly, in the fourth step, depicted in FIG. 16 d, all transmissionsfrom sector 2 in both paths may occur in the same ninth time slot; andall transmissions from sector 3 in both paths may occur in the sametenth time slot. Similarly, in the fifth step, depicted in FIG. 16 e,all transmissions in both paths may occur in the same eleventh timeslot. Finally, in the sixth step, depicted in FIG. 16 f, alltransmissions in both paths may occur in the same twelfth time slot.

In other embodiments of solar tracker wireless monitoring and trackingarrangements 1720 a-f depicted in FIGS. 17 a-f, a repeater/collectorsscheme of data collection may be performed in conjunction with anytopology. Arrangement 1720 a (FIG. 17 a) includes a central data controlsystem (DCS) 1722 a which is located within a matrix of rows and columnsof trackers 1724 a. Four substantially equally-spaced repeaters orintermediate data collectors 1792 a are dispersed among trackers 1724 a,substantially equally-spaced from DCS 1722 a. In a second embodiment ofa solar tracker wireless monitoring and tracking arrangement 1720 billustrated in FIG. 17 b, trackers 1724 b are arranged in concentricrings surrounding a central data control system (DCS) 1722 b. Thus, thesolar plant may have trackers arranged either in a rectangular grid orin concentric circles as shown in FIGS. 17 a-b. Five substantiallyequally-spaced repeaters or intermediate data collectors 1792 b aredispersed among trackers 1724 b, substantially equally-spaced from DCS1722 b.

A third embodiment of a solar tracker wireless monitoring and trackingarrangement 1720 c illustrated in FIG. 17 c is substantially similar toarrangement 1720 a, except that arrangement 1720 c includes eightrepeaters or intermediate data collectors 1792 c disposed in acrisscross pattern. In the particular illustrated embodiment, fourrepeaters 1792 c are horizontally aligned with DCS 1722 c, with thesefive elements being substantially equally spaced apart. Four otherrepeaters 1792 c are vertically aligned with DCS 1722 c, with these fiveelements also being substantially equally spaced apart.

A fourth embodiment of a solar tracker wireless monitoring and trackingarrangement 1720 d illustrated in FIG. 17 d is substantially similar toarrangement 1720 b, except that arrangement 1720 d includes eightrepeaters or intermediate data collectors 1792 d disposed in acrisscross pattern. In the particular illustrated embodiment, fourrepeaters 1792 d are substantially horizontally aligned with DCS 1722 d,with these five elements being substantially equally spaced apart. Fourother repeaters 1792 d are substantially vertically aligned with DCS1722 c, with these five elements also being substantially equally spacedapart.

A fifth embodiment of a solar tracker wireless monitoring and trackingarrangement 1720 e illustrated in FIG. 17 e is substantially similar toarrangement 1720 c, except that the eight repeaters or intermediate datacollectors 1792 e of arrangement 1720 e are disposed in adiagonally-oriented crisscross pattern with respect to the rectangularmatrix of trackers 1724 e.

A sixth embodiment of a solar tracker wireless monitoring and trackingarrangement 1720 f illustrated in FIG. 17 f is substantially similar toarrangement 1720 d, except that the eight repeaters or intermediate datacollectors 1792 f of arrangement 1720 f are disposed in a crisscrosspattern wherein the crisscrossing lines of repeaters 1792 f are notstrictly perpendicular to each other. Rather, the crisscrossing lines ofrepeaters 1792 f may form angles of about 80 degrees and 100 degreestherebetween. Moreover, the innermost four repeaters 1792 f are disposedfarther radially outward than the four repeaters 1792 d of arrangement1720 d.

The dedicated repeaters or intermediate collector nodes 1792 a-f mayexpedite data collection and/or enable better performance. Any or all ofrepeaters 1792 a-f may include multiple radios in order to transmitsignals to several nodes simultaneously on different channels. Any orall of repeaters 1792 a-f may also include directional antennas whichmay provide the repeater with a greater transmission range such that therepeater may more reliably transmit signals to other intermediatecollectors 1792 a-f or to the final data collector 1722 a-f. Theplacement of repeaters 1792 a-f may be dependent on the topology oftrackers 1724 a-f; hardware constraints of trackers 1724 a-f; and onother performance requirements.

The schemes discussed above for data collection may also be employed fordata distribution from the DCS to the trackers. More particularly, inother embodiments depicted in FIGS. 17 a-d and 18 a-d, the inventionprovides schemes for data communication from the DCS to the trackers.

Generally, data communication from the DCS to the trackers can be ofthree types. In the first type, the DCS needs to enquire or otherwisecommunicate with a particular tracker. In the second type, the DCS needsto broadcast the same data to all the trackers. In the third type, theDCS needs to send individual data to every tracker.

In the cases of the first type, in which the DCS needs toenquire/communicate with a particular tracker, communication may befaster than with the other two types and may depend on the depth of thetree/network. The path from the DCS to the tracker may be the same asthe path from the tracker to the DCS, and may include one or moreintermediate nodes. Also, it may be possible to employ an algorithm thatdetermines the shortest distance path between the DCS and the trackerbased on the communication range of the tracker.

In the cases of the second type, in which the DCS needs to broadcast thesame data to all trackers, an intermediate set of nodes can bepre-defined as repeaters for these messages. This allocation of certainnodes as repeaters can be either pre-defined or random depending on thetopology and the communication scheme deployed. Pre-defined allocationof certain nodes as repeaters can be performed for topologies asdiscussed above with regard to embodiments depicted in FIGS. 11 a-f, 14,15 a-g and 16 a-f. In these cases, cluster heads and repeaters mayforward the broadcast packets. For other cases, random mechanisms forallocating certain nodes as repeaters can be deployed. Given theconnectivity graph and the base station, an optimal scheduling of thenodes with no collisions occurring is possible by using some fixednumber of frequency channels such that all nodes receive the message asfast as possible. An example of this scheme is illustrated in FIGS. 18a-d, wherein at every step only selected nodes rebroadcast the data fromthe DCS.

In a first transmission time slot, depicted in FIG. 18 a, DCS 1822transmits to six tracker nodes 1806 a-f. Each of the six transmissionsmay be in a same third of three frequency channels.

In a second transmission time slot, depicted in FIG. 18 b, tracker node1806 a transmits in a first frequency channel to tracker nodes 1806 g-h;tracker node 1806 d transmits in a second frequency channel to trackernodes 1806 i-j; and tracker node 1806 f transmits in the third frequencychannel to tracker nodes 1806 k-r. In the second transmission time slot,each of tracker nodes 1806 a, 1806 d and 1806 f may transmit the sameinformation received in the first transmission time slot, as well asother information already possessed by tracker nodes 1806 a, 1806 d and1806 f.

In a third transmission time slot, depicted in FIG. 18 c, tracker node18061 transmits in the first frequency channel to tracker nodes 1806s-t; tracker node 1806 q transmits in the second frequency channel totracker node 1806 u; and tracker node 1806 h transmits in the thirdfrequency channel to tracker nodes 1806 v-w. In the third transmissiontime slot, each of tracker nodes 1806 l, 1806 q and 1806 h may transmitthe same information received in the second transmission time slot, aswell as other information already possessed by tracker nodes 1806 l,1806 q and 1806 h.

In a fourth transmission time slot, depicted in FIG. 18 d, tracker node1806 t transmits in the third frequency channel to tracker node 1806 x.In the fourth transmission time slot, tracker node 1806 t may transmitthe same information received in the third transmission time slot, aswell as other information already possessed by tracker node 1806 t. U.S.Pat. No. 7,738,455 (serial application Ser. No. 11/488,380) toKeshavarzian et al. discloses details on how the above-described schememay be implemented, and is hereby incorporated by reference herein inits entirety.

In the cases of the third type, in which the DCS needs to sendindividual data to every tracker, individual communication from the DCSto all trackers may take the same amount of time as taken by datacollection by the DCS from the trackers. The time slot lengths mayremain the same while the schedule of hops may be the inverse oropposite of the schedule of hops used in data collection, as illustratedin FIGS. 19 a-d, 20 a-d and 21 a-d. In each of FIGS. 19 a-d, 20 a-d and21 a-d, transmission in a first frequency channel is depicted by a solidarrow, and transmission in a second frequency channel is depicted by adashed arrow.

FIGS. 19 a-d illustrate data collection from tracker nodes to a DCS 1922along two adjacent paths. In the first time slot, depicted in FIG. 19 a,tracker nodes 1906 a-b transmit to tracker nodes 1906 c-d, respectively.The time slot may have a length corresponding to one overhead (header)byte per packet and one data byte per tracker.

In the second time slot, depicted in FIG. 19 b, tracker nodes 1906 c-dtransmit to tracker nodes 1906 e-f, respectively. The time slot may havea length corresponding to one overhead (header) byte per packet and twodata byte per tracker, as nodes 1906 c-d may transmit both theinformation received in the first time slot as well as the informationalready possessed by nodes 1906 c-d.

In the third time slot, depicted in FIG. 19 c, tracker node 1906 etransmits to DCS 1922. The time slot may have a length corresponding toone overhead (header) byte per packet and three data bytes per tracker,as node 1906 e may transmit the information received from both nodes1906 a and 1906 c as well as the information already possessed by node1906 e.

In the fourth time slot, depicted in FIG. 19 d, tracker node 1906 ftransmits to DCS 1922. The time slot may have a length corresponding toone overhead (header) byte per packet and three data bytes per tracker,as node 1906 f may transmit the information received from both nodes1906 b and 1906 d as well as the information already possessed by node1906 f. Accordingly, for data collection from the tracker nodes to theDCS, the total duration of all four time slots may correspond to fouroverhead bytes and nine data bytes.

In contrast to FIGS. 19 a-d, FIGS. 20 a-d illustrate one embodiment of adata communication scheme from the DCS to each tracker node in theparallel data paths. In the first time slot, depicted in FIG. 20 a, DCS2022 transmits to tracker node 2006 f. The time slot may have a lengthcorresponding to one overhead (header) byte and three data bytes, asdata for each of tracker nodes 2006 b, 2006 d and 2006 f is beingtransmitted.

In the second time slot, depicted in FIG. 20 b, DCS 2022 transmits totracker node 2006 e. The time slot may have a length corresponding toone overhead (header) byte and three data bytes, as data for each oftracker nodes 2006 a, 2006 c and 2006 e is being transmitted.

In the third time slot, depicted in FIG. 20 c, tracker node 2006 etransmits to tracker node 2006 c; and tracker node 2006 f transmits totracker node 2006 d. The time slot may have a length corresponding toone overhead (header) byte per packet and two data bytes, as data foreach of tracker nodes 2006 a, 2006 c is being transmitted by trackernode 2006 e, and data for each of tracker nodes 2006 b, 2006 d is beingtransmitted by tracker node 2006 f.

In the fourth time slot, depicted in FIG. 20 d, tracker node 2006 ctransmits to tracker node 2006 a; and tracker node 2006 d transmits totracker node 2006 b. The time slot may have a length corresponding toone overhead (header) byte per packet and one data byte, as data foronly tracker node 2006 a is being transmitted by tracker node 2006 c,and data for only tracker node 2006 b is being transmitted by trackernode 2006 d. Accordingly, for data collection from the DCS to thetracker nodes, the total duration of all four time slots may correspondto four overhead bytes and nine data bytes, which is the same as thetime duration for data collection from the tracker nodes to the DCS.

In contrast to FIGS. 19 a-d, FIGS. 21 a-d illustrate another embodimentof a data communication scheme from the DCS to each tracker node in theparallel data paths. In the first time slot, depicted in FIG. 21 a, DCS2122 transmits to tracker node 2106 f. The time slot may have a lengthcorresponding to one overhead (header) byte and three data bytes, asdata for each of tracker nodes 2106 b, 2106 d and 2106 f is beingtransmitted.

In the second time slot, depicted in FIG. 21 b, DCS 2122 transmits totracker node 2106 e. The time slot may have a length corresponding toone overhead (header) byte and three data bytes, as data for each oftracker nodes 2106 a, 2106 c and 2106 e is being transmitted. Also inthe second time slot, tracker node 2106 f transmits to tracker node 2106d. However, the time required for the transmission from tracker node2106 f corresponds to only one overhead byte and two data bytes, as datafor tracker nodes 2106 b, 2106 d is being transmitted by tracker node2106 f, and this shorter time period does not affect the overall timeneeded for the second time slot.

In the third time slot, depicted in FIG. 21 c, tracker node 2106 etransmits to tracker node 2106 c; and tracker node 2106 d transmits totracker node 2106 b. The time slot may have a length corresponding toone overhead (header) byte per packet and two data bytes, as data foreach of tracker nodes 2106 a, 2106 c is being transmitted by trackernode 2106 e. However, the time required for the transmission fromtracker node 2106 d corresponds to only one overhead byte and one databyte, as data for only tracker node 2106 b is being transmitted bytracker node 2106 d, and this shorter time period does not affect theoverall time needed for the second time slot.

In the fourth time slot, depicted in FIG. 21 d, tracker node 2106 ctransmits to tracker node 2106 a. The time slot may have a lengthcorresponding to one overhead (header) byte per packet and one databyte, as data for only tracker node 2106 a is being transmitted bytracker node 2106 c. Accordingly, for data collection from the DCS tothe tracker nodes, the total duration of all four time slots maycorrespond to four overhead bytes and nine data bytes, which again isthe same as the time duration for data collection from the tracker nodesto the DCS.

Referring to FIGS. 20 a and 21 a, the DCS sends data for all threetrackers nodes in the bottom row or lower communication path. In thenext step shown in FIGS. 20 c and 21 b, the receiving node (2006 f and2106 f, respectively) extracts its data and transmits the rest of thedata to the next node along the path and so on. As demonstrated in FIGS.19 a-d, 20 a-d, 21 a-d, the DCS-to-trackers individual communicationschedule can be the reverse of the trackers-to-DCS data collectionschedule, and may yield the same performance. If the schedule of datacollection by the DCS is optimal, then the individual communicationschedule to the tracker nodes may also be optimal.

An advantage of such a multiple collection schedule, random slottedscheme is that it is faster than other methods, and thus moretime-efficient. Another advantage is that the scheme may keep all nodesbusy. Links unused in the first round/time slot may be used insubsequent rounds/time slots. Yet another advantage is that the schememay be more reliable and robust. The schedule may be computed such thateach node receives the message from different sources in differentrounds/time slots. A further advantage of the scheme is that it is easyto implement. That is, nodes may simply follow a pre-computed schedule.U.S. Pat. No. 7,738,455 (serial application Ser. No. 11/488,380) toKeshavarzian et al. discloses details on how such a scheme may beimplemented, and is hereby incorporated by reference herein in itsentirety.

One embodiment of a wireless communication method 2200 of the inventionis illustrated in FIG. 22. In a first step 2202, a matrix of trackers isprovided. The matrix includes rows and columns of trackers. For example,in the embodiment of FIG. 4 a, a matrix of trackers is shown includingcolumns and rows of trackers.

In a next step 2204, a number of rows and a number of columns in thematrix is determined. That is, in the embodiment of FIG. 4 a, it may bedetermined that the matrix includes m number of columns and n number ofrows of trackers.

Next, in step 2206, if the number of rows is substantially greater thanthe number of columns, then vertical sweeping is performed. The verticalsweeping includes passing data along each of the columns of trackers toan end tracker in each column. For example, in the embodiment of FIG. 4a it may be assumed that the number of rows n is substantially greaterthan the number of columns m. As shown in FIG. 4 a, vertical sweepingmay be performed wherein trackers in row i=1 transmit information tocorresponding trackers immediately below in row i=2. The trackers in rowi=2 then pass information to corresponding trackers immediately below inrow i=3 and so on until all information is transmitted to the endtrackers in the bottom row i=n.

In step 2208, if the number of rows is substantially less than thenumber of columns, then horizontal sweeping is performed. The horizontalsweeping includes passing data along each of the rows of trackers to anend tracker in each row. For example, in the embodiment of FIG. 4 b itmay be assumed that the number of rows n is substantially less than thenumber of columns m. As shown in FIG. 4 b, horizontal sweeping may beperformed wherein trackers in column j=1 transmit information tocorresponding trackers immediately to the right in column j=2. Thetrackers in column j=2 then pass information to corresponding trackersimmediately to the right in column j=3 and so on until all informationis transmitted to the end trackers in the rightmost column j=m.

In a next step 2210, if the number of rows is substantially equal to thenumber of columns, then diagonal sweeping is performed. The diagonalsweeping includes passing data diagonally across each of the rows andcolumns of trackers to an end tracker in each row and each column. Forexample, in the embodiment of FIGS. 4 c-e it may be assumed that thenumber of rows n is substantially equal to the number of columns m. Asshown in FIG. 4 c, diagonal sweeping may be performed wherein trackersin row i=1 and/or column j=1 (except for the end trackers at row i=1,column j=m and at row i=n, column j=1) transmit information tocorresponding trackers immediately diagonally adjacent to the lowerright in column j=2 and/or row i=2. The trackers in column row i=2and/or j=2 (except for one end tracker at row i=2, column km and anotherend tracker at row i=n, column j=2) then pass information tocorresponding trackers immediately diagonally adjacent to the lowerright in column j=3 and/or row i=3. This process continues, as shown inFIG. 4 e, for example, until all information is transmitted to the endtrackers in the rightmost column j=m and/or the bottom row i=n.

In a final step 2212, the data is passed along the end trackers to afinal destination data collector. For example, as shown in FIG. 4 d, theend tracker at row i=1, column j=m transmits to the end trackerimmediately below at row i=2, column j=m; and the end tracker at rowi=n, column j=1 transmits to the end tracker immediately to the right atrow i=n, column j=2. Further, as shown in FIG. 4 e, the end tracker atrow i=2, column j=m transmits to the end tracker immediately below atrow i=3, column j=m; and the end tracker at row i=n, column j=2transmits to the end tracker immediately to the right at row i=n, columnj=3. This process continues until all data has been passed to a finaldestination data collector 226 c.

Another embodiment of a method 2300 of the invention for wirelesscommunication is illustrated in FIG. 23. In a first step 2302, aplurality of trackers are provided disposed within a substantiallycircular outer boundary. For example, as shown in FIG. 9 a, trackers 906are provided within a substantially circular outer imaginary boundary903.

In a next step 2304, a final destination data collector is providedapproximately centrally located within the circular outer boundary. Forexample, as shown in FIG. 9 a, a final destination data collector 922 isprovided approximately centrally located within the circular outerboundary 903.

Next, in step 2306, the trackers are divided or grouped into a pluralityof substantially pie-shaped sectors. Each pie-shaped sector is definedbetween the circular outer boundary and two corresponding imaginary andsubstantially radially-oriented borders. That is, as shown in FIG. 9 a,trackers 906 are grouped or divided into six pie-shaped sectors 902 a-f.Each of pie-shaped sectors 902 a-f is defined between the circular outerboundary 903 and a respective pair of corresponding imaginary andsubstantially radially-oriented borders. Each respective pair of bordersis an adjacent two of radially-oriented borders 904 a-f.

In step 2308, circumferential sweeping is performed within each sector.The circumferential sweeping within each sector includes passing datafrom ones of the trackers disposed along a first of theradially-oriented borders to a plurality of end trackers disposed alonga second of the radially-oriented borders. The passing is in a pluralityof circumferential directions. For example, as shown in FIG. 9 a, datawithin sector 902 a is passed by the trackers that are adjacent toradially-oriented border 904 a, including trackers 906 a, 906 c and 906e, in circumferential directions generally indicated by arcuate arrow926. As further shown in FIGS. 9 b-e, the data transmissions in thecircumferential directions continue until all data has been received bythe end trackers adjacent to radially-oriented border 904 b. Similarpatterns of data transmission also occur in the other sectors 902 b-f.

In a final step 2310, the data is passed along the end trackers to thefinal destination data collector. As shown in FIGS. 9 f-k, data ispassed sequentially from end tracker 906 g to end tracker 906 h; thenfrom end tracker 906 h to end tracker 906 i; then from end tracker 906 ito end tracker 906 j; then from end tracker 906 j to end tracker 906 k;then from end tracker 906 k to end tracker 906 l; and finally from endtracker 906 l to data collector 922.

Another embodiment of a method 2400 of the invention for wirelesscommunication is illustrated in FIG. 24. In a first step 2402, aplurality of trackers are provided disposed within a substantiallycircular outer boundary. For example, as shown in FIG. 10 a, trackers1006 are provided within a substantially circular outer imaginaryboundary 1003.

In a next step 2404, a final destination data collector is providedapproximately centrally located within the circular outer boundary. Forexample, as shown in FIG. 10 a, a final destination data collector 1022is provided approximately centrally located within the circular outerboundary 1003.

Next, in step 2406, the trackers are divided or grouped into a pluralityof substantially pie-shaped sectors. Each pie-shaped sector is definedbetween the circular outer boundary and two corresponding imaginary andsubstantially radially-oriented borders. That is, as shown in FIG. 10 a,trackers 1006 are divided or grouped into six pie-shaped sectors 1002a-f. Each of pie-shaped sectors 1002 a-f is defined between the circularouter boundary 1003 and a respective pair of corresponding imaginary andsubstantially radially-oriented borders. Each respective pair of bordersis an adjacent two of radially-oriented borders 1004 a-f.

In step 2408, the trackers in one of the sectors are divided or groupedinto a plurality of substantially parallel and substantiallyradially-oriented lines of trackers. A first of the lines of trackers isdisposed along a first of the radially-oriented borders. Each of theother lines of trackers extend substantially from the circular outerboundary to a second of the radially-oriented borders. For example, asshown in FIG. 10 a, the trackers in sector 1002 a may be divided orgrouped into a first line of trackers disposed along radially-orientedborder 1004 a and including tracker 1006 a as its radially outermosttracker. A second line of trackers includes tracker 1006 c as itsradially outermost tracker and includes tracker 1006 g, which isadjacent to radially-oriented border 1004 b. Similarly, a third line oftrackers extends from tracker 1006 h to tracker 1006, etc.

In a next step 2410, substantially radial sweeping is performed withineach line in the one sector. The substantially radial sweeping includespassing data in directions away from the circular outer boundary to aplurality of end trackers disposed along the second radially-orientedborder. For example, as shown in FIGS. 10 a-e, data within sector 1002 ais passed in generally radially inward directions from the trackers thatare adjacent to outer border 1003, including trackers 1006 a, 1006 c and1006 h, along their respective lines of trackers to the end trackersdisposed adjacent to radially-oriented border 1004 b, including endtrackers 1006 g and 1006 i.

In a final step 2412, the data is passed along the end trackers to thefinal destination data collector. As shown in FIGS. 10 a and 10 c-g,data is passed sequentially from end tracker 1006 e along the endtrackers adjacent to radially-oriented border 1004 b until arriving attracker 1006 i, tracker 1006 g, and finally at data collector 1022.

While this invention has been described as having an exemplary design,the invention may be further modified within the spirit and scope ofthis disclosure. This application is therefore intended to cover anyvariations, uses, or adaptations of the invention using its generalprinciples.

What is claimed is:
 1. A method of wireless communication, the methodcomprising the steps of: providing a final destination data collector;providing a plurality of trackers disposed to one side of the finaldestination data collector, the trackers being arranged in a sequentialdata path such that each of said plurality of trackers is configured topass data to the final destination data collector or to another of saidplurality of trackers that is closer to the final destination datacollector; dividing the sequential data path into a plurality ofsectors, each of said plurality of sectors including a subset of theplurality of trackers, each of said plurality of sectors including a farend and a close end, the far end being farther from the finaldestination data collector than is the close end; simultaneouslybeginning transmission of the data from the far end of each of saidplurality of sectors towards the close end of each of said plurality ofsectors along the sequential data path; continuing the transmission ofthe data along the sequential data path such that each of said pluralityof trackers transmits its own data in addition to data received from animmediately preceding tracker of said plurality of trackers, thetransmission continuing until the data from a first of said plurality ofsectors that is closest to the final destination data collector has beentransmitted to the final destination data collector; transmitting thedata from a second of said plurality of sectors that is second closestto the final destination data collector to the first of said pluralityof sectors; and passing the data from the second of said plurality ofsectors along trackers in the first of said plurality of sectors to thefinal destination data collector, the trackers in the first of saidplurality of sectors refraining from adding their data to the data fromthe second of said plurality of sectors during the passing.
 2. Themethod of claim 1, wherein at least one of the trackers that receivesthe passed data also produces original data, and the at least one of thetrackers passes both the passed data received by the at least one of thetrackers and the original data produced by the at least one of thetrackers.
 3. The method of claim 1, wherein all of the data istransmitted at a same frequency.
 4. The method of claim 1, wherein thedata is transmitted at two different frequencies along two parallelsequential data paths.
 5. The method of claim 1, further comprising thestep of transmitting the data from a third of said plurality of sectorsthat is third closest to the final destination data collector to thesecond of said plurality of sectors.
 6. The method of claim 5, furthercomprising the step of passing the data from the third of said pluralityof sectors along the trackers in the first of said plurality of sectorsand the second of said plurality of sectors to the final destinationdata collector, the trackers in the first of said plurality of sectorsand the second of said plurality of sectors refraining from adding theirdata to the data from the third of said plurality of sectors during thepassing.